Atmospheric sulfate aerosols have important impacts on air quality, climate, and human and ecosystem health. However, current air-quality models generally underestimate the rate of conversion of ...sulfur dioxide (SO₂) to sulfate during severe haze pollution events, indicating that our understanding of sulfate formation chemistry is incomplete. This may arise because the air-quality models rely upon kinetics studies of SO₂ oxidation conducted in dilute aqueous solutions, and not at the high solute strengths of atmospheric aerosol particles. Here, we utilize an aerosol flow reactor to perform direct investigation on the kinetics of aqueous oxidation of dissolved SO₂ by hydrogen peroxide (H₂O₂) using pH-buffered, submicrometer, deliquesced aerosol particles at relative humidity of 73 to 90%. We find that the high solute strength of the aerosol particles significantly enhances the sulfate formation rate for the H₂O₂ oxidation pathway compared to the dilute solution. By taking these effects into account, our results indicate that the oxidation of SO₂ by H₂O₂ in the liquid water present in atmospheric aerosol particles can contribute to the missing sulfate source during severe haze episodes.
Atmospheric amines – Part I. A review Ge, Xinlei; Wexler, Anthony S.; Clegg, Simon L.
Atmospheric environment (1994),
2011, 2011-1-00, 20110101, Letnik:
45, Številka:
3
Journal Article
Recenzirano
Amines are emitted by a wide range of sources and are ubiquitous atmospheric organic bases. Approximately 150 amines and about 30 amino acids have been identified in the atmosphere. We review the ...present knowledge of atmospherically relevant amines with respect to their sources, fluxes, and dynamics including gas-phase reactions, gas-to-particle conversion and deposition. The health effects of aliphatic and aromatic amines are briefly summarized as well as the atmospheric occurrence and reactivity of amino acids and urea.
► 154 amines, 32 amino acids and urea have been identified in the atmosphere. ► Sources, fluxes, and dynamics of atmospheric amines and amino acids are reviewed. ► Health effects of aliphatic and aromatic amines are briefly summarized.
Amines enter the atmosphere from a wide range of sources, but relatively little is known about their atmospheric behavior, especially their role in gas/particle partitioning. In Part I of this work (
...Ge et al., 2011) a total of 154 amines, 32 amino acids and urea were identified as occurring in the atmosphere, based upon a survey of the literature. In this work we compile data for the thermodynamic properties of the amines which control gas/particle partitioning (Henry’s Law constant, liquid vapor pressure, acid dissociation constant, activity coefficient and solubility in water), and also estimate the solid/gas dissociation constants of their nitrate and chloride salts. Prediction methods for boiling point, liquid vapor pressure, acid dissociation constant and the solubility of the amines in water are evaluated, and used to estimate values of the equilibrium constants where experimental data are lacking. Partitioning of amines into aqueous aerosols is strongly dependent upon pH and is greatest for acidic aerosols. For several common amines the tendency to partition to the particle phase is similar to or greater than that of ammonia. Our results are presented as tables of values of thermodynamic equilibrium constants, which are also incorporated into the Extended Aerosol Inorganics Model (
E-AIM,
http://www.aim.env.uea.ac.uk/aim/aim.php) to enable gas/aerosol partitioning and other calculations to be carried out.
► Thermodynamic data of amines that controls gas/particle partitioning are compiled. ► Data includes HLC, vapor pressure, activity coefficient and aqueous solubility. ► Partitioning of amines into aqueous aerosols is strongly dependent upon pH. ► Amines can partition into the aerosol, similar to or greater than that of ammonia.
Using a comparative evaporation kinetics approach, we describe a new and accurate method for determining the equilibrium hygroscopic growth of aerosol droplets. The time-evolving size of an aqueous ...droplet, as it evaporates to a steady size and composition that is in equilibrium with the gas phase relative humidity, is used to determine the time-dependent mass flux of water, yielding information on the vapor pressure of water above the droplet surface at every instant in time. Accurate characterization of the gas phase relative humidity is provided from a control measurement of the evaporation profile of a droplet of know equilibrium properties, either a pure water droplet or a sodium chloride droplet. In combination, and by comparison with simulations that account for both the heat and mass transport governing the droplet evaporation kinetics, these measurements allow accurate retrieval of the equilibrium properties of the solution droplet (i.e., the variations with water activity in the mass fraction of solute, diameter growth factor, osmotic coefficient or number of water molecules per solute molecule). Hygroscopicity measurements can be made over a wide range in water activity (from >0.99 to, in principle, <0.05) on time scales of <10 s for droplets containing involatile or volatile solutes. The approach is benchmarked for binary and ternary inorganic solution aerosols with typical uncertainties in water activity of <±0.2% at water activities >0.9 and ∼±1% below 80% RH, and maximum uncertainties in diameter growth factor of ±0.7%. For all of the inorganic systems examined, the time-dependent data are consistent with large values of the mass accommodation (or evaporation) coefficient (>0.1).
The Acidity of Atmospheric Particles and Clouds Pye, Havala O T; Nenes, Athanasios; Alexander, Becky ...
Atmospheric chemistry and physics,
04/2020, Letnik:
20, Številka:
8
Journal Article
Recenzirano
Odprti dostop
Acidity, defined as pH, is a central component of aqueous chemistry. In the atmosphere, the acidity of condensed phases (aerosol particles, cloud water, and fog droplets) governs the phase ...partitioning of semi-volatile gases such as HNO
, NH
, HCl, and organic acids and bases as well as chemical reaction rates. It has implications for the atmospheric lifetime of pollutants, deposition, and human health. Despite its fundamental role in atmospheric processes, only recently has this field seen a growth in the number of studies on particle acidity. Even with this growth, many fine particle pH estimates must be based on thermodynamic model calculations since no operational techniques exist for direct measurements. Current information indicates acidic fine particles are ubiquitous, but observationally-constrained pH estimates are limited in spatial and temporal coverage. Clouds and fogs are also generally acidic, but to a lesser degree than particles, and have a range of pH that is quite sensitive to anthropogenic emissions of sulfur and nitrogen oxides, as well as ambient ammonia. Historical measurements indicate that cloud and fog droplet pH has changed in recent decades in response to controls on anthropogenic emissions, while the limited trend data for aerosol particles indicates acidity may be relatively constant due to the semi-volatile nature of the key acids and bases and buffering in particles. This paper reviews and synthesizes the current state of knowledge on the acidity of atmospheric condensed phases, specifically particles and cloud droplets. It includes recommendations for estimating acidity and pH, standard nomenclature, a synthesis of current pH estimates based on observations, and new model calculations on the local and global scale.
Adsorption isotherms have important practical applications, including in solution chemistry where they have been used to model solvent and solute activities in liquid mixtures at extreme ...concentrations, such as pure melts. The conventional Brunauer–Emmett–Teller (BET) and Guggenheim–Anderson–de Boer (GAB) models are less successful for dilute solutions (high water activities), for which most data are available. In this work we extend these models to include arbitrary numbers of additional adsorbed monolayers and, using statistical mechanics, derive expressions for the Gibbs energies of solutions and for solute and solvent activities. We demonstrate consistency with results that can be obtained by other methods, and show how a particular simple case is equivalent to Raoult’s law. Test applications of the equations to water activity data for aqueous solutions over very wide ranges of concentration show that the addition of a single extra adsorbed layer to the fitted adsorption model greatly increases its accuracy, especially for low concentrations.
A semiempirical model is presented that predicts surface tensions (σ) of aqueous electrolyte solutions and their mixtures, for concentrations ranging from infinitely dilute solution to molten salt. ...The model requires, at most, only two temperature-dependent terms to represent surface tensions of either pure aqueous solutions, or aqueous or molten mixtures, over the entire composition range. A relationship was found for the coefficients of the equation σ = c1 + c2 T (where T (K) is temperature) for molten salts in terms of ion valency and radius, melting temperature, and salt molar volume. Hypothetical liquid surface tensions can thus be estimated for electrolytes for which there are no data, or which do not exist in molten form. Surface tensions of molten (single) salts, when extrapolated to normal temperatures, were found to be consistent with data for aqueous solutions. This allowed surface tensions of very concentrated, supersaturated, aqueous solutions to be estimated. The model has been applied to the following single electrolytes over the entire concentration range, using data for aqueous solutions over the temperature range 233−523 K, and extrapolated surface tensions of molten salts and pure liquid electrolytes: HCl, HNO3, H2SO4, NaCl, NaNO3, Na2SO4, NaHSO4, Na2CO3, NaHCO3, NaOH, NH4Cl, NH4NO3, (NH4)2SO4, NH4HCO3, NH4OH, KCl, KNO3, K2SO4, K2CO3, KHCO3, KOH, CaCl2, Ca(NO3)2, MgCl2, Mg(NO3)2, and MgSO4. The average absolute percentage error between calculated and experimental surface tensions is 0.80% (for 2389 data points). The model extrapolates smoothly to temperatures as low as 150 K. Also, the model successfully predicts surface tensions of ternary aqueous mixtures; the effect of salt−salt interactions in these calculations was explored.
Alkylaminium sulfates originate from the neutralisation reaction between short-chained amines and sulfuric acid and have been detected in atmospheric aerosol particles. Their physicochemical ...behaviour is less well characterised than their inorganic equivalent, ammonium sulfate, even though they play a role in atmospheric processes such as the nucleation and growth of new particles and cloud droplet formation. In this work, a comparative evaporation kinetics experimental technique using a cylindrical electrodynamic balance is applied to determine the hygroscopic properties of six short-chained alkylaminium sulfates, specifically mono-, di-, and tri-methylaminium sulfate and mono-, di-, and tri-ethyl aminium sulfate. This approach allows for the retrieval of a water-activity-dependent growth curve in less than 10 s, avoiding the uncertainties that can arise from the volatilisation of semi-volatile components. Measurements are made on particles > 5 µm in radius, avoiding the need to correct equilibrium measurements for droplet-surface curvature with assumed values of the droplet-surface tension. Variations in equilibrium solution droplet composition with varying water activity are reported over the range 0.5 to > 0.98, along with accurate parameterisations of solution density and refractive index. The uncertainties in water activities associated with the hygroscopicity measurements are typically < ±0.2 % at water activities > 0.9 and ∼ ±1 % below 0.9, with maximum uncertainties in diameter growth factors of ±0.7 %. Comparison with previously reported measurements show deviation across the entire water activity range.
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